Flutter version auto-updating in DevTools

This is an action item from the postmortem review for https://github.com/flutter/devtools/issues/9701

If DevTools was running integration tests on WASM (https://github.com/flutter/devtools/issues/9727) **and** DevTools was still updating the pinned Flutter version everyday, we could have caught this within a day of [the regression ](https://github.com/flutter/devtools/issues/9701) landing in Flutter.

Details for why this was removed in the first place at b/340303879

Inizia leggendo l’issue di postmortem collegata 9701 e l’issue WASM integration-test 9727, quindi esamina la motivazione indicata in b/340303879. Il lavoro è completato quando la versione di Flutter bloccata di DevTools viene nuovamente aggiornata automaticamente, in modo che i test di integrazione WASM possano rilevare tempestivamente le regressioni di Flutter.

Scritto dal modello di indicizzazione a partire dal testo della issue.